1. Field of the Invention
This invention relates to an image forming device utilizing a laser beam.
2. Discussion of the Background
A laser printer is known which includes output means for outputting a laser beam having an intensity modulated according to an input data, a photosensitive recording medium, and an image forming optical system disposed to receive the laser beam from the output means for irradiating the laser beam on the recording medium, thereby to form an image constituted of dots on the recording medium.
Since the laser beam is a Gaussian beam having an intensity distribution nearly of a Gaussian distribution mode, it is necessary to provide an overlapping portion in each adjacent two dots in order to form a solid image. In this case, when the printing is performed, for example, with a dot size of 60 .mu.m and a resolution of 400 dpi (scanning distance of about 60 .mu.m), the beam intensity distribution on the recording medium is as shown in FIG. 1. Thus, an irregularity is caused in density of the solid image corresponding to the irregularity in the beam intensity. Jitters are also caused.
To cope with this problem, JP-A-58-152269 proposes a laser beam printer in which the overlapping portion of adjacent dots is increased to minimize the irregularity in intensity as shown in FIG. 2. While the above technique is effective to produce good solid images with uniform density, another problem is caused. Namely, when a pattern having high and low density is intended, the difference therebetween is unavoidably averaged and reduced as shown in FIG. 3. In other words, it is impossible to produce an image with density gradation faithful to the input data.